by Sharon Jayson, USA TODAY

by Sharon Jayson, USA TODAY

As many as 11% of U.S. women ages 15-44 who have ever had sexual intercourse have used a "morning after" pill at least once, according to the first federal report on emergency contraception, out Thursday.

That's 5.8 million women -- and half say they used it because they feared their birth control method may have failed. The rest say they had unprotected sex.

The National Center for Health Statistics analysis is based on responses collected through in-person interviews with 12,279 women from 2006-2010. Of those, 10,605 said they were sexually experienced.

The FDA approved emergency contraceptive pills in 1998 for use up to five days after intercourse. But experts say there are plenty of obstacles to widespread use.

"There's not a whole lot of information out there about it," says Beth Jordan Mynett, medical director of the Association of Reproductive Health Professionals, based in Washington, D.C. "There are price issues and access issues and they are not insubstantial. It's not universally stocked and available."

The report finds that 23% of sexually experienced women ages 20â??24 had ever used emergency contraception, compared with 16% ages 25â??29 and 14% ages 15â??19. Just 5% of women 30â??44 said they had ever used it, which the report notes may be due to it not being approved during their early reproductive years.

The report shows that emergency contraception was most common among women 20-24, the never married, Hispanic and white women, and the college-educated.

The fact that half of the women used emergency contraception because they worried their contraceptive didn't work suggests that "women are concerned they don't have access to highly effective, long-acting methods," says Deborah Nucatola of Los Angeles, an OB-GYN in clinical practice and senior director of medical services at Planned Parenthood.

But use of IUDs and implants is growing, and it will reduce concern about contraceptive failure, she says. "Women using IUDs and implants don't have to remember to do anything. Women using the pill, patch or ring have to remember to do something every day, every week or every month," she says.

Mynett, an internist whose clinical practice is in women's health, says the "morning after pill" should not be confused with the "abortion pill."

"Emergency contraception does not cause an abortion. You take emergency contraception pills to largely prevent ovulation from happening. This is pregnancy prevention," she says. "The abortion pill stops a pregnancy that's already existing. The abortion pill is taken after you already know you're pregnant and it's given by a health care provider."

In a separate report, the agency, part of the Centers for Disease Control and Prevention, also analyzed contraception use since 1982. The report comes out at a time when contraceptive coverage under the Affordable Care Act is being challenged by some religious and business groups.

Among findings on contraceptive use trends:

-- 99% of sexually-experienced women have used at least one contraceptive method.

-- Nearly 30% have used five or more methods.

-- 82% of sexually-experienced women have ever used the pill -- a percentage that's remained stable since 1995.

-- Condom use (by a male partner) has jumped from 52% in 1982 to 93% in 2006-10.

Claire Brindis, director of the Bixby Center for Global Reproductive Health at the University of California, San Francisco, says the report points out women's need for different contraceptive alternatives over the years.

"The fact that women may need to use four or five or six different methods in their lives ... points to me to the importance of having many contraceptive options available for women," she says.

By the numbers

-- 93.4% of sexually-experienced women have used condoms.

-- 23% have used Depo-Provera, a three-month injectable contraceptive.